Timber is used to a substantial extent in the construction industry. It is necessary that for this use the strength of the timber is known accurately. The dangers are obvious if the timber is too weak. On the other hand if adequate grading apparatus is not available, rough and ready techniques based on experience will often result in overgrading so that timber which is of adequate strength will be rejected.
A timber grader (as disclosed in South African patent specification No. 71/8601) has been developed to grade timber. The timber plank is placed on a pair of support rolls and pressure applied mid-way between the supports. The force needed for a particular deflection is measured to give an indication of the strength of the timber (as an alternative the deflection for a particular force may provide such indication). A timber plank is so tested at various positions along its length. In order to find the strength in the opposite direction, the plank has to be turned over and the measuring operation repeated. It will be seen that this process is very time consuming and can only be used as a sampling technique.